Currently, in order to recover energy generated in braking as regenerative energy, a regenerative cooperative control is performed. The regenerative cooperative control generates a regenerative brake, instead of a service brake, when a brake pedal is depressed by a driver. When the regenerative cooperative control is performed, an input piston is moved by the depression of the brake pedal. At this time, if the input piston contact with an output piston (master cylinder (hereinafter, referred to as M/C) piston provided in M/C) to generate M/C pressure, a braking force of the service brake is generated, so that a regenerative efficiency is to be decreased.
In view of the above, JP-A-2007-55588 proposes a braking device for a vehicle, in which a clearance expecting a stroke amount corresponding to a brake amount of the regenerative brake is provided between the input piston and the output piston. Since the clearance is provided between the input piston and the output piston, the input piston does not contact with the output piston until the maximum regenerative brake to be generated is generated while the regenerative cooperation, so that it is possible to achieve the maximum regenerative efficiency.
However, in power source failure in which an electrical system (e.g., brake ECU) is out of order, the output piston is required to be directly pressed to generate the braking force, and thus the clearance between the input piston and the output piston becomes an ineffective stroke. Accordingly, it causes a response delay at the time of brake operation, and the brake fluid to be output from the M/C to a wheel cylinder (hereinafter, referred to as W/C) may be not sufficient in accordance with a size of the clearance.